1. Field of the Invention
This invention relates to an electroluminescence device (hereinafter merely referred to as EL device) utilizing an electroluminescence phenomenon (hereinafter merely referred to as EL phenomenon).
2. Description of the Prior Art
The EL phenomenon is the phenomenon in which an electric field is applied to a sort of fluorescent substance to obtain a light emission. Since the EL device utilizing the EL phenomenon is light weight and thin, it has been heretofore generally used as a back light such as a liquid crystal display device.
FIG. 5 shows one example of an EL device of an organic dispersed type wherein a fluorescent powder 5 is dispersed into a resin 6 to form a light emitting layer 3, to which is applied an AC electric field to emit light.
The EL device of the organic dispersed type has a transparent electrode 2 formed of indium tin oxide (ITO), a light emitting layer 3 and an opposed electrode 4 formed of aluminum or the like, which are stacked in that order on one surface of a transparent substrate 1 formed of glass or the like. The light emitting layer 3 is formed by dispersing fluorescent powders 5 wherein active agents such as Cu, Mn, TbF.sub.3, SmF.sub.3, etc. are suitably added into a base material such as a mixed crystal of ZnS or ZnS and ZnSe according to an emitting color to form a center of light emission, into a resin 6 such as fluoroplastics, polyvinyl alcohol (PVA), polycarbonate (PC).
An AC electric field of 50 Hz-10 kHz in the order of 10.sup.4 V/cm, for example, is applied between the transparent electrode 2 and the opposed electrode 4 to emit light.
The electric field/luminance characteristics in 400 Hz of the EL device structured as described above is shown in FIG. 6.
In the EL device as described above, in a case where a matrix display takes place, it is necessary that a multiplex drive is effected between an electric field E.sub.1 (hereinafter merely referred to electric field E.sub.1) of a selective segment and an electric field E.sub.2 (hereinafter merely referred to as an electric field E.sub.2) of a non-selective segment to increase a contrast B.sub.1 : B.sub.2 between a luminance B.sub.1 in the electric field E.sub.1 and a luminance B.sub.2 in the electric field E.sub.2. (See FIG. 6.)
However, in the electric field/luminance characteristics of the EL device as constructed above, the degree of curve of the luminance to the applied electric field is small for each frequency, and therefore, there was an inconvenience in that a contrast sufficient to obtain a clear matrix display is not obtained due to the light emitted by a cross talk produced in the non-selective segment.